The present invention relates to a data processing apparatus.
In a known electronic register, input data is stored in a memory and predetermined data processing is performed by using the stored data. In an AC power ON mode, a DC voltage derived from the AC power source is supplied to the memory. However, in an AC power OFF mode, an output voltage from a back-up battery is supplied to the memory. For this reason, even in the AC power OFF mode, storage data in the memory is backed up or retained.
In a conventional battery back-up system of this type, when the AC power is kept off for a long period of time, e.g., a summer vacation, the voltage of the back-up battery often becomes lower than an operating voltage. When the output voltage from the back-up battery is lower than the operating voltage, the storage contents of the memory may be lost or destroyed.
In a conventional electronic register, even if the storage contents of the memory have become indefinite, normal register operation can be restored upon ON operation of the AC power source. In this case, new data is written in addition to the error data already stored in the memory. For this reason, the new input data may also be invalid.